What are the possible reasons for an increase in bot signups and how to detect/prevent them?
Michael Ko
Co-founder & CEO, Suped
Published 24 Apr 2025
Updated 16 Aug 2025
8 min read
A sudden surge in bot signups can be a frustrating and alarming experience for any business. It skews your analytics, wastes resources, and can severely impact your email deliverability. Understanding why these automated signups occur is the first step toward effective mitigation.
These aren't just minor annoyances; they represent a real threat to your data integrity, sender reputation, and overall email marketing effectiveness. Identifying and addressing the root causes is crucial to protecting your online presence.
Reasons for increased bot signups
The intentions behind bot signups
One common reason for an influx of bot signups is subscription bombing, a malicious tactic designed to harass the recipient. In these attacks, bots sign up a victim's email address to numerous newsletters and services, overwhelming their inbox with unwanted emails. The goal is often to distract the victim from critical alerts, such as fraudulent activity on their financial accounts. This type of attack can lead to high bounce rates for your emails, signaling to mailbox providers that your list quality is poor, which can ultimately harm your email list deliverability.
Bots may also sign up to harvest data or to test for vulnerabilities. They might be trying to gather valid email addresses for future spam campaigns or to perform credential stuffing attacks, where stolen username and password combinations are automatically tried across various websites. If your signup form is linked to a login process, bots might attempt to test these credentials, even if the password field isn't immediately visible to a human user.
Another common scenario involves SEO spammers or poorly configured bots. Some bots are programmed to look for forms that resemble blog comment sections, hoping to inject spammy links or content onto your site. If your signup form has a generic structure, a bot might mistake it for a comment form and proceed with automated submissions, regardless of the actual purpose of the form. These bots often do not care about the specifics of your signup process, only that a form exists for submission.
In rarer cases, bot signups can be part of a targeted attack, perhaps by a competitor, aiming to sabotage your email marketing efforts or test your infrastructure's resilience. Flooding your system with fake signups can overwhelm your servers, reveal system weaknesses, or even trigger security alerts that waste your team's time and resources. Understanding these diverse motivations helps in devising comprehensive defense strategies.
How to identify bot activity
Spotting the signs of automated signups
Detecting bot signups often requires a keen eye on your data and unusual patterns. A sudden, unexplained spike in signups, particularly during off-peak hours (like the middle of the night in your local timezone), is a significant red flag. You might also notice a dramatic drop in your subscription confirmation rates, as these bot-generated emails are typically invalid or never opened. This signals that a large portion of your new signups aren't real users completing the double opt-in process.
Technical indicators can provide strong evidence of bot activity. Pay close attention to the IP addresses from which signups originate; a high volume from the same IP, or from IPs associated with Virtual Private Servers (VPS) or known data centers, is highly suspicious. Bots can also use rotating User-Agent strings to mimic different browsers or devices, so look for patterns that don't match your typical user behavior or a high diversity of seemingly random User-Agents. These anomalies are key in learning how to identify spambot sign-ups.
Analyzing the email addresses themselves can also reveal patterns. Bots often use disposable email services, random character strings, or domains that are not commonly used by your legitimate audience. While it can be challenging to find a single, consistent pattern if the bots are sophisticated, observing these collective characteristics across a large number of signups helps confirm that you are dealing with automated, non-human traffic.
Strategies for prevention
Implementing robust bot prevention measures
One of the most effective strategies to prevent bot signups is implementing a double opt-in process. This requires new signups to click a confirmation link sent to their email address before being added to your list. While some worry about a slight drop in conversion rates, the quality of your list drastically improves, as it largely filters out invalid or bot-generated email addresses. For more on this, check out how you can prevent bots from submitting forms.
Incorporating CAPTCHA challenges, such as reCAPTCHA, into your signup forms can significantly deter bots. Modern CAPTCHAs, especially invisible ones, offer a balance between security and user experience. They analyze user behavior in the background to distinguish between humans and bots without always requiring a visible challenge. While some internal teams might initially resist due to conversion concerns, the improved list quality and reduced deliverability issues often outweigh these trade-offs, as legitimate conversion rates can actually improve by filtering out fake entries.
Honeypot fields are another clever, user-friendly technique. These are hidden fields in your form that are invisible to human users but are detected and filled out by bots. If the honeypot field is filled, you know it's a bot submission and can discard it without any impact on your genuine users. This method effectively catches less sophisticated bots that simply fill in all available fields. Understanding the purpose of bot signups can help you select the most appropriate prevention methods for your website, as outlined in what are the purposes of bots.
For more advanced protection, consider leveraging Web Application Firewalls (WAFs) or specialized bot management services. Services like Cloudflare can detect and block suspicious traffic at the connection level, often before it even reaches your website. They use advanced fingerprinting and threat intelligence gathered across their vast networks to identify and mitigate automated attacks, protecting your forms from both simple and sophisticated bot operations.
Impact on email deliverability
Protecting your sender reputation
Bot signups can have a detrimental impact on your email deliverability and sender reputation. When your lists are filled with invalid or inactive email addresses, your bounce rates will soar. High bounce rates signal to Internet Service Providers (ISPs) that your sending practices are poor, which can lead to your emails being directed to spam folders or even blocked entirely. Similarly, if bots sign up using real email addresses that belong to unsuspecting users, those users might mark your emails as spam, further damaging your reputation. It's vital to understand how bot signups impact deliverability.
Maintaining a clean email list is paramount for healthy deliverability. A significant volume of bot-generated signups can lead to your sending IP address or domain being placed on an email blocklist (or blacklist). Once on a blocklist, your emails are likely to be rejected by many mailbox providers, severely impacting your ability to reach legitimate subscribers. Regularly monitoring your list for suspicious contacts and promptly removing them is just as important as implementing proactive prevention measures. Learn what happens when your domain is blocklisted.
Conclusion
A proactive approach to email security
Addressing bot signups is an ongoing process that requires continuous monitoring and adaptation. By understanding the motivations behind these attacks, implementing robust detection methods, and deploying multiple layers of prevention, you can significantly reduce the impact of bot activity on your email lists and protect your sender reputation. A proactive stance ensures your legitimate subscribers receive your emails, maintaining the integrity and effectiveness of your communication channels.
Views from the trenches
Best practices
Always implement double opt-in to verify new signups, ensuring they are genuine users.
Use invisible reCAPTCHA or honeypot fields on all signup forms to filter out automated submissions.
Monitor your signup data for unusual patterns in volume, timing, and IP addresses.
Regularly clean your email lists by removing unengaged subscribers and invalid addresses.
Common pitfalls
Relying on a single bot prevention method, as sophisticated bots can often bypass simple defenses.
Ignoring a sudden spike in signups, which can lead to poor deliverability and reputation damage.
Failing to analyze audit trails and traffic metadata for signs of bot activity.
Prioritizing signup quantity over quality, leading to a list filled with fake or inactive contacts.
Expert tips
A/B test the impact of CAPTCHA on your conversion rates to find the optimal balance.
Leverage advanced bot management services like Cloudflare to block suspicious traffic at the network level.
Analyze email domains and User-Agent strings to identify non-human or suspicious signup patterns.
Be aware that bots can also be used for malicious purposes, like distracting from fraudulent activity.
Expert view
Expert from Email Geeks says some bots don't realize they are signing up; they submit forms hoping they are comments, often with links.
March 19, 2021 - Email Geeks
Marketer view
Marketer from Email Geeks says subscription bombing is a common tactic to harass recipients, and occasionally, it's competitive sabotage.
